Although microspheres of chitosan crosslinked with 8-hydroxyquinoline-5-sulphonic acid can act as an adsorbent for several

metallic ions (Vitali et al., 2008), the interference was greatly minimised Linsitinib concentration by the application of the pre-concentration potential. At −0.4 V, the potential chosen to pre-concentrate Cu(II), the metallic ions with a reduction potential more negative than −0.4 V are not reduced (pre-concentrated) at the electrode surface. These results show that the proposed sensor can be used for Cu(II) determination in solutions containing the tested ions without a notable loss in the analytical response. The anodic stripping voltammograms for different Cu(II) concentrations under the optimised conditions are shown in Fig. 4. In the inset, the respective calibration curve obtained is represented, while the validation parameters obtained GSI-IX supplier for Cu(II) determination employing the CPE-CTS are given in Table 1. From these data it can be seen that the current peak increases linearly with increasing Cu(II) concentration in the range of 5.0 × 10−7 to 1.4 × 10−5 mol L−1 (Δip = −0.70 + 0.12 × 107 [Cu(II)], r = 0.9990). However, for higher Cu(II) concentrations a negative deviation

from linearity was observed due to the electrode surface saturation. Also, a slight shift toward more positive potentials is observed in the peak potential with increasing Cu(II) concentration. The detection and quantification limits calculated ( Table 1) show that the proposed sensor has a high sensitivity toward Cu(II) detection. The relative enough standard deviation (n = 8) was lower than 3.0% for the determination of Cu(II) in solutions with concentrations of 6.0 × 10−6, 5.0 × 10−5 and 1.5 × 10−4 mol L−1

indicating that the electrode provides reliable data with excellent precision. In this study, the concentration of 1.5 × 10−4 mol L−1 Cu(II) is out of the linear range of the calibration curve, however, the relative standard deviation was practically the same as those observed for the other concentrations lying within the calibration curve. This behaviour indicates that the electrode provides reliable data even for solutions with concentrations slightly higher than those of the calibration curve. The repeatability for ten measurements of the current peak for solutions of 5.0 × 10−5 mol L−1 Cu(II) under optimised conditions was excellent, with relative standard deviations of 1.31%. The reproducibility of the current peak was tested over four days using different solutions prepared in the concentration of 5.0 × 10−5 mol L−1 Cu(II). The relative standard deviation was 2.73%. When compared to other modified carbon paste electrodes employed for Cu(II) determination, the CPE-CTS sensor also showed good performance. For example, a carbon paste electrode modified with 3,4-dihydro-4,4,6-trimethyl-2(1H)-pyrimidine thione for use in potentiometry showed a linear range of 9.8 × 10−7 to 7.